This application is based on and claims priority from Japanese Application No. HEI 3-352370 filed Dec. 13, 1991, the disclosure of which is incorporated by reference herein.
The present invention relates to a film applying method and a film applying apparatus, and more particularly relates to a film applying method and a film applying apparatus, in each of which a base plate is conveyed, and first and second film feed members, opposed to the upper and lower sides of the base plate, which attract leading edges of films and which are then moved toward the leading edges of the upper and lower sides of the base plate conveyed to a film applying position, to tentatively apply the leading edges of the films to the leading edges of the base plate. Thereafter, the films are completely applied to the base plate under pressure by pressure applying rollers so that each of the films completely applied to the sides of the plate has a length corresponding to that of the plate.
Generally, a printed circuit board for an electronic machine such as a computer has wirings made of copper or the like in a prescribed pattern on one or both sides of an electrically insulating base plate. In manufacturing the printed circuit board, a stratified film consisting of a photosensitive resin layer, which is a photoresist layer, and a light-transmissible resin film, which is a protective film for protecting the layer, is first applied, under heat and pressure, to an electroconductive layer which is a thin copper film provided on the base plate. The heat and pressure applying operation is performed by mass production by a film applying apparatus. Thereafter, a wiring pattern film is overlaid on the stratified film. Then, the photosensitive resin layer is exposed to light through the wiring pattern film and the light-transmissible resin film for a prescribed time.
Thereafter, the light-transmissible resin film is peeled from the base plate by a peeling unit, and the photosensitive resin layer exposed to the light is developed to make an etching mask pattern. The unnecessary portions of the electroconductive layer are removed by etching, and the remaining portions of the photosensitive resin layer are removed. Thus, the printed circuit board having wirings in the prescribed pattern is manufactured. For such film applying apparatuses, various systems have been proposed including those disclosed in the Japan Patent Applications (OPI) Nos. 208037/88 and 7344/91 filed by the present applicant (the term "OPI" as used herein means an "unexecuted published application").
FIG. 12 is a side view of such a conventional film applying apparatus which illustrates the structure and operation thereof. Since the apparatus is nearly symmetrical upwardly and downwardly from a conveyance passage for an electrically insulating base plate, only the upper half of the apparatus is shown in FIG. 12.
In the apparatus, a three-layer stratified film 1 consisting of three layers which are a light-transmissible resin film, a photosensitive resin layer and a second light-transmissible resin film is continuously wound on a supply roller 2 in advance. The film 1 is unwound from the supply roller 2 so that a film separation roller 3 separates the film into the light-transmissible resin film 1A and a stratified film 1B consisting of the second light-transmissible resin film and the photosensitive resin layer exposed on one side thereof, which is to be applied to the base plate.
The separated stratified film 1B is supplied to the surface of a main vacuum suction plate 5 (which is a film feed member) along a tension roller 9. An auxiliary vacuum suction plate 13 and a cutter 14 are provided at the feed passage for the film 1B downstream of the suction plate 5 with regard to the film feed direction. A vacuum suction bar 15 and a pressure applying roller 16 are provided at the feed passage for the film 1B downstream of the cutter 14. The suction plate 5 tentatively applies the film 1B to an electroconductive layer on the base plate 6 while holding the film on the suction plate by vacuum suction.
The suction plate 5 is supported by a support member to be movable upwardly and downwardly. The support member 7 can be moved toward and away from the base plate 6 in directions B. The support member 7 is attached with a guide member 8 to the body frame 9 of the apparatus so that the support member can be moved in the directions B while sliding on the guide member. A pair of such support members 7 are provided above and below the base plate conveyance passage so that the support members are moved upwardly and downwardly in conjunction with each other through a rack-and-pinion mechanism by a first driver (not shown in FIG. 12). The mechanism includes racks 7A provided on the support members 7, and a pinion 7B engaged with the racks and supported by the body frame 9 of the apparatus.
The suction plate 5 is supported by the support member 7 so that the plate can be moved toward and away from the base plate 6 in directions C independently of the movement of the support member by a second driver 11, such as a pneumatic cylinder, through a rack-and-pinion mechanism provided on a support member 12. The mechanism includes a first rack 12A secured to the support member 7, a pinion 12B engaged with the rack to be moved upwardly and downwardly along the rack by the driver 11, and a second rack 12C engaged with the pinion to be moved upwardly and downwardly in parallel with the first rack. The suction plate 5 has a tentatively-applying downstream end portion 5A in which a heater 5B is provided.
To tentatively apply the film 1B to the base plate 6 by the suction plate 5, the end portion 5A is moved to the vicinity of the base plate or into contact therewith as the film remains wound on the end portion. At that time, the end portion 5A is heated by the heater 5B to tentatively apply the leading edge of the film 1B to the base plate 6 under heat and pressure.
The auxiliary vacuum suction plate 13 attracts the leading edge of the film 1B to hold the film at the edge on the end portion 5A of the suction plate 5 to tentatively apply the film to the base plate 6. Accordingly, the suction plate 13 is moved toward and away from the feed passage for the film 1B in directions D by a driver 13A such as a pneumatic cylinder, which is fastened to the support member 7.
The cutter 14 is opposed to the suction plate 13 across the feed passage for the film 1B to cut the film 1B to a length corresponding to that of the base plate 6.
A pair of pressure applying rollers 16 also are provided above and below the base plate conveyance passage. The upper and lower films 1B tentatively applied to the base plate 6 are pinched thereon under prescribed pressure by the rollers 16 and also are heated by the rollers so that the films are completely applied to the base plate.
To move the suction plate 5 of the conventional film applying apparatus, the support member 7 not only must be moved, but also the second driver 11 and the rack-and-pinion mechanism which are provided on the support member must be moved together with the support member. Thus, the load on the first driver for the support member 7 is so heavy that the main vacuum suction plate cannot be moved quickly. This hinders the rapid operation of the apparatus and restricts the processing capacity thereof. This is a problem.
Further, since not only the support member 7 and the first driver but also various other devices, such as the second driver and the rack-and-pinion mechanism, must be provided to move the suction plate 5, the structure of the apparatus is complicated. This also is a problem.
Additionally, the upper and lower suction plates 5 are usually moved by pneumatic cylinders independently of each other. Thus, when the cylinders are supplied with air having the same pressure, a downward force acts on each of the upper and lower suction plates 5 due to gravity so that it is difficult to operate the plates synchronously, and the tentative pressure applying force of the upper suction plate is made stronger than that of the lower one.
To prevent this problem, the air pressure for the upper and lower pneumatic cylinders is regulated to operate the upper and lower suction plates 5 synchronously. However, precisely regulating the pressure in such a manner is difficult. Alternatively, the problem can be prevented by stopping the lower suction plate in a prescribed position by a stopper or the like during the upward movement of the suction plate, and the air pressure in the cylinder for the suction plate is somewhat increased. However, the tentative pressure applying force of the lower suction plate rises to make it difficult to equalize the power of the upper and lower suction plates.